The invention relates to a burst cap, especially for a hybrid inflater, comprising a bottom and a sleeve-like side wall delimiting an igniter compartment inside the burst cap, the burst cap being adapted to be pressurized with compressed gas on its outside in the idle mode and, in the case of operation, being adapted to be destroyed by a bursting pressure on the side of the igniter compartment. In addition, the invention relates to a hybrid inflator, an airbag module and a vehicle safety system. Moreover, the invention relates to a method of manufacturing a burst cap.
Occupant restraint systems for automotive vehicles usually include airbag modules comprising an airbag which in the case of crash is inflated so as to reduce the probability of body parts of a vehicle occupant colliding with a vehicle component. In order to inflate the airbag in the case of crash, for example hybrid inflators consisting of a compressed gas tank containing compressed gas and/or fluids and a pyrotechnical subassembly are provided, the pyrotechnical subassembly serving for triggering and/or heating the gas which is originally compressed and will escape in the case of operation. The compressed gas of such hybrid inflator can be closed off In a pressure-tight manner toward the pyrotechnical subassembly by a burst diaphragm or by a burst cap which in the idle mode thus can be or is pressurized on its outer peripheral side with the compressed gas stored in the compressed gas tank. The term “in the idle mode” hereby means that the hybrid inflator has not yet been activated, or in other words, that the burst cap is in an idle position in which no activating signal is provided as yet in response to which the burst cap is to be opened or burst.
WO 01/13484 A1, especially FIG. 8, illustrates an afore-described burst cap which is incorporated in a hybrid inflator. The cup-shaped burst cap includes a bottom which at its boundary area is transformed into a sleeve-like side wall and/or is integrally connected to the same by forming a radius. The bottom and the sleeve-like side wall delimit an igniter compartment in which an igniter is accommodated, wherein in the idle mode the burst cap can be or is pressurized with compressed gas on its outer peripheral side. In the case of operation, the burst cap can be destroyed by a bursting pressure on the igniter compartment side by activating the igniter. The burst cap has a continuously constant material thickness.
Such hybrid inflator thus comprises a compressed gas tank which may be filled, for example at room temperature, with a gas or gas mixture having a predetermined pressure, e.g. 580 bar, for example when manufacturing the hybrid inflator. Such pressure or filling pressure may increase, in the idle mode of the hybrid inflator, in the so called high-temperature case, by heating a vehicle interior to e.g. 90° C. by solar radiation to a maximum filling pressure of approx. 800 bar. When an airbag is triggered, the pyrotechnical subassembly opens the burst diaphragm closing the compressed gas tank or the burst cap closing the compressed gas tank so that the gas pre-compressed in the compressed gas tank inflates the airbag, wherein the pre-compressed gas may be nitrogen, argon, helium or oxygen and/or a mixture of two or more of said gases.
In the case of operation in which the burst cap is to be opened by activating an igniter, said igniter for this purpose has to build up a bursting pressure on the igniter compartment side which is far above the tilling pressure prevailing in the compressed gas tank. The igniter does not only have to build up the pressure required for the destruction of the burst cap, when considered isolated per se, but in addition it has to “counteract” the filling pressure prevailing in the compressed gas tank, i.e. overcome such counter-pressure so as to cause destruction of the burst cap at all, when it is incorporated in such hybrid inflator.
Since the pressure in such compressed gas tank may increase to approx. 800 bar as above described, extremely high bursting pressures have been necessary so far to open closing diaphragms and/or to open a burst cap. Accordingly, both a burst cap closing the gas tank and a possibly provided diaphragm are subjected to high pressure on the side of the compressed gas tank in the idle mode so that a burst cap is exposed, for example, to extreme bending and deformations and may support against or rest on other components of the hybrid inflator or the gas module thus possibly having a negative effect. Moreover and in addition the burst cap must be very stable by having appropriate material thickness so as to withstand the afore-described maximum filling pressure in the idle mode.